ENV to macports

[Joshua Root]

Timothy Lee wrote:
> I thought choosing which version was an either/or scenario.
> Are you saying that its possible to choose more than one per build?

They are actually just variants under the hood. The only difference
compared to normal variants is that platform variants are automatically
selected based on the platform you're building on. Selecting platform
variants manually is normally a really bad idea, but if you need to
target a different platform, it just might work in some cases.

- Josh